Automotive coating compositions exhibiting a metallic appearance are well known in the coatings art. The metallic appearance can be produced by using a metallic pigment such as metal flake in the coating composition. A metallic appearance can also be produced by the inclusion of metallic-like pigments such as metal oxide coated mica pigment in the coating composition, as disclosed in U.S. Pat. Nos. 4,499,143, 4,605,687, and 4,598,015, which are incorporated herein by reference.
Multicoat coating compositions comprising a pigmented basecoat and at least one clear topcoat are described in, for example, U.S. Pat. Nos. 4,705,839 and 4,791,168. The use of a basecoat-clear topcoat multicoat coating system results in improved aesthetic appearance along with improved resistance to weathering and damage.
In the one-coat system, no clearcoat or topcoat is applied. This more economical process is most useful on trucks, buses and fleet car body parts.
Automotive coating compositions exhibiting an opalescent color effect may be formulated using a three layer coating comprising first, a basecoat having an N-4 to N-8 value on the Munsell color chart, an interference or intermediary coating containing metal oxide encapsulated mica particles in a pigment to binder ratio of 0.06 to 0.13, and a third substantially clear outer topcoat. These opalescent coating systems are disclosed in U.S. Pat. Nos. 4,539,258 and 4,615,940 which are incorporated by reference. The application of three separate paint layers, however, makes the coating process complex and more expensive than the two coat process.
An opalescent color effect can be produced in a two-coat system using coating compositions comprising a thermoplastic or thermosetting resin, transparent metal oxide pigments having a particle size of about 20 nm to about 30 nm and metallic or metallic-like pigments. These opalescent coating compositions are exemplified in U.S. Pat. No. 4,753,829 which is incorporated by reference. However, the opalescence so produced exhibits a sharp and distinct color, having dramatic and unnatural complimentary color shifts and color travel.
Accordingly, there has been a need in the pigment art for simplified methods of producing opalescence which result in more natural hues, softer colors and minimal color travel.